The present invention relates to a closure device for specimen containers such as test tubes to be used with ultra-centrifuges. The closure device comprises a cap having an insertion portion which is adopted to be securely positioned in the open end of a test tube. The outer diameter of the lower part of the insertion portion which is adopted to be inserted into the test tube corresponds to the inner diameter of the tube.
Conventional closure devices for test tubes used in fixed-angle rotors of ultracentrifuge devices usually comprise an insertion portion which is adopted to be introduced into the open end of a test tube and a clamping means for clamping the test tube edge in the closure device thereby providing a firm, seal-tight connection between the test tube and the closure device. The lower portion of the insertion member is cylindrical and has an outer diameter corresponding to the inner diameter of the test tube. Said lower portion is introduced into the test tube. The upper portion on the insertion member is also cylindrical and contains a thin, threaded projection. To close the test tube, a clamping means is provided. The clamping means comprises a cover which has an outwardly or inwardly sloping conical surface and the cover is screwed to the thin threaded projection on the insertion member by a corresondingly-threaded nut. The cover's conical surface presses against the test tube edge either inwardly against a corresponding conical surface at the top edge of the cylindrical region of the insertion member, or outwardly, by means of an O-ring, against a correspondingly cylindrical projection on the cover.
Such common conventional closure devices have the disadvantage of being relatively expensive, owing to the number of individual parts which they comprise. In addition, a relatively large amount of time and work is required to screw the cover to the insertion member. An additional disadvantage is that a special screwing tool must be available.